Gippsland/Melbourne Transmission Reco Recommend

[chefo]

Hi, Currently run a 347w connected to a C4 auto with the standard 3.2 rear diff in my GT Capri. Im finding the RPM at 70kph+ too much (near 4500 around 100kph). Im looking to get recommendations for both which box and where to get it done. The 347w is pretty tame. I'd be happy with an auto or manual. I hear a bit of talk about tremec 5 speeds and AOD transmissions and Im keen to hear any thoughts.

Thanks